Homozygous mutation, p.Pro304His, in IDH3A, encoding isocitrate dehydrogenase subunit is associated with severe encephalopathy in infancy

Mitochondrial encephalopathies are a heterogeneous group of disorders which generally carries a grave prognosis. Using exome sequencing, we identified a homozygous mutation, Pro-304-His in the IDH3A gene, in a patient suffering from infantile encephalopathy with peripheral and autonomic nervous system involvement. Mammalian isocitrate dehydrogenase (IDH) 3 is a heterotetramer of 2alfa, 1beta, and 1gamma subunits, and IDH3A encodes the alfa subunit of the mitochondrial NAD(+)-dependent IDH. Here we show that in contrast to wild-type human IDH3A, the human IDH3A which harbor the p.Pro304His mutation does not complement the yeast Delta idh1/Delta idh2 growth defect on ethanol-acetate. We therefore propose that homozygosity for the p.Pro304His mutation is deleterious for mitochondrial NAD(+)-specific IDH3A activity in human. IDH3A now joins the list of TCA cycle-related proteins, which includes ACO2, DLD, SLC25A19, FH, and succinate dehydrogenase subunits, all associated with neurological disorders.